Network Working Group F. Le Faucheur, Ed.
Request for Comments: 4804 Cisco Systems, Inc.
Category: Standards Track February 2007
Aggregation of Resource ReSerVation Protocol (RSVP)Reservations over MPLS TE/DS-TE Tunnels
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
RFC 3175 specifies aggregation of Resource ReSerVation Protocol
(RSVP) end-to-end reservations over aggregate RSVP reservations.
This document specifies aggregation of RSVP end-to-end reservations
over MPLS Traffic Engineering (TE) tunnels or MPLS Diffserv-aware
MPLS Traffic Engineering (DS-TE) tunnels. This approach is based on
RFC 3175 and simply modifies the corresponding procedures for
operations over MPLS TE tunnels instead of aggregate RSVP
reservations. This approach can be used to achieve admission control
of a very large number of flows in a scalable manner since the
devices in the core of the network are unaware of the end-to-end RSVP
reservations and are only aware of the MPLS TE tunnels.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 20071. Introduction
The Integrated Services (Intserv) [INT-SERV] architecture provides a
means for the delivery of end-to-end Quality of Service (QoS) to
applications over heterogeneous networks.
[RSVP] defines the Resource reSerVation Protocol that can be used by
applications to request resources from the network. The network
responds by explicitly admitting or rejecting these RSVP requests.
Certain applications that have quantifiable resource requirements
express these requirements using Intserv parameters as defined in the
appropriate Intserv service specifications ([GUARANTEED],
[CONTROLLED]).
The Differentiated Services (DiffServ) architecture ([DIFFSERV]) was
then developed to support the differentiated treatment of packets in
very large scale environments. In contrast to the per-flow
orientation of Intserv and RSVP, Diffserv networks classify packets
into one of a small number of aggregated flows or "classes", based on
the Diffserv codepoint (DSCP) in the packet IP header. At each
Diffserv router, packets are subjected to a "per-hop behavior" (PHB),
which is invoked by the DSCP. The primary benefit of Diffserv is its
scalability. Diffserv eliminates the need for per-flow state and
per-flow processing, and therefore scales well to large networks.
However, DiffServ does not include any mechanism for communication
between applications and the network. Thus, as detailed in
[INT-DIFF], significant benefits can be achieved by using Intserv
over Diffserv including resource-based admission control, policy-
based admission control, assistance in traffic
identification/classification, and traffic conditioning. As
discussed in [INT-DIFF], Intserv can operate over Diffserv in
multiple ways. For example, the Diffserv region may be statically
provisioned or RSVP aware. When it is RSVP aware, several mechanisms
may be used to support dynamic provisioning and topology-aware
admission control, including aggregate RSVP reservations, per-flow
RSVP, or a bandwidth broker. The advantage of using aggregate RSVP
reservations is that it offers dynamic, topology-aware admission
control over the Diffserv region without per-flow reservations and
the associated level of RSVP signaling in the Diffserv core. In
turn, this allows dynamic, topology-aware admission control of flows
requiring QoS reservations over the Diffserv core even when the total
number of such flows carried over the Diffserv core is extremely
large.
[RSVP-AGG] and [RSVP-GEN-AGG] describe in detail how to perform such
aggregation of end-to-end RSVP reservations over aggregate RSVP
reservations in a Diffserv cloud. They establish an architecture
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
where multiple end-to-end RSVP reservations sharing the same ingress
router (Aggregator) and egress router (Deaggregator) at the edges of
an "aggregation region" can be mapped onto a single aggregate
reservation within the aggregation region. This considerably reduces
the amount of reservation state that needs to be maintained by
routers within the aggregation region. Furthermore, traffic
belonging to aggregate reservations is classified in the data path
purely using Diffserv marking.
[MPLS-TE] describes how MPLS Traffic Engineering (TE) tunnels can be
used to carry arbitrary aggregates of traffic for the purposes of
traffic engineering. [RSVP-TE] specifies how such MPLS TE tunnels
can be established using RSVP-TE signaling. MPLS TE uses
Constraint-Based Routing to compute the path for a TE tunnel. Then,
Admission Control is performed during the establishment of TE tunnels
to ensure they are granted their requested resources.
[DSTE-REQ] presents the Service Providers requirements for support of
Diffserv-aware MPLS Traffic Engineering (DS-TE). With DS-TE,
separate DS-TE tunnels can be used to carry different Diffserv
classes of traffic, and different resource constraints can be
enforced for these different classes. [DSTE-PROTO] specifies RSVP-TE
signaling extensions as well as OSPF and Intermediate System to
Intermediate System (IS-IS) extensions for support of DS-TE.
In the rest of this document we will refer to both TE tunnels and
DS-TE tunnels simply as "TE tunnels".
TE tunnels have much in common with the aggregate RSVP reservations
used in [RSVP-AGG] and [RSVP-GEN-AGG]:
- A TE tunnel is subject to Admission Control and thus is
effectively an aggregate bandwidth reservation.
- In the data plane, packet scheduling relies exclusively on
Diffserv classification and PHBs.
- Both TE tunnels and aggregate RSVP reservations are controlled
by "intelligent" devices on the edge of the "aggregation core"
(Head-end and Tail-end in the case of TE tunnels; Aggregator and
Deaggregator in the case of aggregate RSVP reservations.
- Both TE tunnels and aggregate RSVP reservations are signaled
using the RSVP protocol (with some extensions defined in
[RSVP-TE] and [DSTE-PROTO] respectively for TE tunnels and DS-TE
tunnels).
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
This document provides a detailed specification for performing
aggregation of end-to-end RSVP reservations over MPLS TE tunnels
(which act as aggregate reservations in the core). This document
builds on the RSVP Aggregation procedures defined in [RSVP-AGG] and
[RSVP-GEN-AGG], and only changes those where necessary to operate
over TE tunnels. With [RSVP-AGG] and [RSVP-GEN-AGG], a lot of
responsibilities (such as mapping end-to-end reservations to
Aggregate reservations and resizing the Aggregate reservations) are
assigned to the Deaggregator (which is the equivalent of the tunnel
Tail-end) while with TE, the tunnels are controlled by the tunnel
Head-end. Hence, the main change over the RSVP Aggregations
procedures defined in [RSVP-AGG] and [RSVP-GEN-AGG] is to modify
these procedures to reassign responsibilities from the Deaggregator
to the Aggregator (i.e., the tunnel Head-end).
[LSP-HIER] defines how to aggregate MPLS TE Label Switched Paths
(LSPs) by creating a hierarchy of such LSPs. This involves nesting
of end-to-end LSPs into an aggregate LSP in the core (by using the
label stack construct). Since end-to-end TE LSPs are themselves
signaled with RSVP-TE and reserve resources at every hop, this can be
looked at as a form of aggregation of RSVP(-TE) reservations over
MPLS TE tunnels. This document capitalizes on the similarities
between nesting of TE LSPs over TE tunnels and RSVP aggregation over
TE tunnels, and reuses the procedures of [LSP-HIER] wherever
possible.
This document also builds on the "RSVP over Tunnels" concepts of RFC2746 [RSVP-TUN]. It differs from that specification in the following
ways:
- This document describes operation over MPLS tunnels, whereas RFC2746 describes operation with IP tunnels. One consequence of
this difference is the need to deal with penultimate hop popping
(PHP).
- MPLS-TE tunnels inherently reserve resources, whereas the
tunnels in RFC 2746 do not have resource reservations by
default. This leads to some simplifications in the current
document.
- This document builds on the fact that there is exactly one
aggregate reservation per MPLS-TE tunnel, whereas RFC 2746
permits a model where one reservation is established on the
tunnel path for each end-to-end flow.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
- We have assumed in the current document that a given MPLS-TE
tunnel will carry reserved traffic and nothing but reserved
traffic, which negates the requirement of RFC 2746 to
distinguish reserved and non-reserved traffic traversing the
same tunnel by using distinct encapsulations.
- There may be several MPLS-TE tunnels that share common Head-end
and Tail-end routers, with the Head-end policy determining which
tunnel is appropriate for a particular flow. This scenario does
not appear to be addressed in RFC 2746.
At the same time, this document does have many similarities with RFC2746. MPLS-TE tunnels are "type 2 tunnels" in the nomenclature of
RFC 2746:
"The (logical) link may be able to promise that some overall level
of resources is available to carry traffic, but not to allocate
resources specifically to individual data flows".
Aggregation of end-to-end RSVP reservations over TE tunnels combines
the benefits of [RSVP-AGG] and [RSVP-GEN-AGG] with the benefits of
MPLS, including the following:
- Applications can benefit from dynamic, topology-aware,
resource-based admission control over any segment of the end-
to-end path, including the core.
- As per regular RSVP behavior, RSVP does not impose any burden on
routers where such admission control is not needed (for example,
if the links upstream and downstream of the MPLS TE core are
vastly over-engineered compared to the core capacity, admission
control is not required on these over-engineered links and RSVP
need not be processed on the corresponding router hops).
- The core scalability is not affected (relative to the
traditional MPLS TE deployment model) since the core remains
unaware of end-to-end RSVP reservations and only has to maintain
aggregate TE tunnels since the datapath classification and
scheduling in the core relies purely on the Diffserv mechanism
(or more precisely the MPLS Diffserv mechanisms, as specified in
[DIFF-MPLS]).
- The aggregate reservation (and thus the traffic from the
corresponding end to end reservations) can be network engineered
via the use of Constraint based routing (e.g., affinity,
optimization on different metrics) and when needed can take
advantage of resources on other paths than the shortest path.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
- The aggregate reservations (and thus the traffic from the
corresponding end-to-end reservations) can be protected against
failure through the use of MPLS Fast Reroute.
This document, like [RSVP-AGG] and [RSVP-GEN-AGG], covers aggregation
of unicast sessions. Aggregation of multicast sessions is for
further study.
2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
3. Definitions
For readability, a number of definitions from [RSVP-AGG] as well as
definitions for commonly used MPLS TE terms are provided here:
Aggregator This is the process in (or associated with) the
router at the ingress edge of the aggregation region
(with respect to the end-to-end RSVP reservation)
and behaving in accordance with [RSVP-AGG]. In this
document, it is also the TE tunnel Head-end.
Deaggregator This is the process in (or associated with) the
router at the egress edge of the aggregation region
(with respect to the end-to-end RSVP reservation)
and behaving in accordance with [RSVP-AGG]. In this
document, it is also the TE tunnel Tail-end
E2E End to end
E2E Reservation This is an RSVP reservation such that:
(i) corresponding Path messages are initiated
upstream of the Aggregator and terminated
downstream of the Deaggregator, and
(ii) corresponding Resv messages are initiated
downstream of the Deaggregator and terminated
upstream of the Aggregator, and
(iii) this RSVP reservation is aggregated over an
MPLS TE tunnel between the Aggregator and
Deaggregator.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
An E2E RSVP reservation may be a per-flow
reservation. Alternatively, the E2E reservation may
itself be an aggregate reservation of various types
(e.g., Aggregate IP reservation, Aggregate IPsec
reservation). See Section 5 and 6 for more details
on the types of E2E RSVP reservations. As per
regular RSVP operations, E2E RSVP reservations are
unidirectional.
Head-end This is the Label Switch Router responsible for
establishing, maintaining, and tearing down a given
TE tunnel.
Tail-end This is the Label Switch Router responsible for
terminating a given TE tunnel.
Transit LSR This is a Label Switch Router that is on the path of
a given TE tunnel and is neither the Head-end nor
the Tail-end.
4. Operations of RSVP Aggregation over TE with Pre-established Tunnels
[RSVP-AGG] and [RSVP-GEN-AGG] support operations both in the case
where aggregate RSVP reservations are pre-established and where
Aggregators and Deaggregators have to dynamically discover each other
and dynamically establish the necessary aggregate RSVP reservations.
Similarly, RSVP Aggregation over TE tunnels could operate both in the
case where the TE tunnels are pre-established and where the tunnels
need to be dynamically established.
In this document we provide a detailed description of the procedures
in the case where TE tunnels are already established. These
procedures are based on those defined in [LSP-HIER]. The routing
aspects discussed in Section 3 of [LSP-HIER] are not relevant here
because those aim at allowing the constraint based routing of end-
to-end TE LSPs to take into account the (aggregate) TE tunnels. In
the present document, the end-to-end RSVP reservations to be
aggregated over the TE tunnels rely on regular SPF routing. However,
as already mentioned in [LSP-HIER], we note that a TE tunnel may be
advertised into IS-IS or OSPF, to be used in normal SPF by nodes
upstream of the Aggregator. This would affect SPF routing and thus
routing of end-to-end RSVP reservations. The control of aggregation
boundaries discussed in Section 6 of [LSP-HIER] is also not relevant
here. This uses information exchanged in GMPLS protocols to
dynamically discover the aggregation boundary. In this document, TE
tunnels are pre-established, so that the aggregation boundary can be
easily inferred. The signaling aspects discussed in Section 6.2 of
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
[LSP-HIER] apply to the establishment/termination of the aggregate TE
tunnels when this is triggered by GMPLS mechanisms (e.g., as a result
of an end-to-end TE LSP establishment request received at the
aggregation boundary). As this document assumes pre-established
tunnels, those aspects are not relevant here. The signaling aspects
discussed in Section 6.1 of [LSP-HIER] relate to the
establishment/maintenance of the end-to-end TE LSPs over the
aggregate TE tunnel. This document describes how to use the same
procedures as those specified in Section 6.1 of [LSP-HIER], but for
the establishment of end-to-end RSVP reservations (instead of end-
to-end TE LSPs) over the TE tunnels. This is covered further in
Section 4 of the present document.
Pre-establishment of the TE tunnels may be triggered by any
mechanisms including; for example, manual configuration or automatic
establishment of a TE tunnel mesh through dynamic discovery of TE
Mesh membership as allowed in [AUTOMESH].
Procedures in the case of dynamically established TE tunnels are for
further studies.
4.1. Reference Model
|----| |----|
H--| R |\ |-----| |------| /| R |--H
H--| |\\| | |---| | |//| |--H
|----| \| He/ | | T | | Te/ |/ |----|
| Agg |=======================| Deag |
/| | | | | |\
H--------//| | |---| | |\\--------H
H--------/ |-----| |------| \--------H
H = Host requesting end-to-end RSVP reservations
R = RSVP router
He/Agg = TE tunnel Head-end/Aggregator
Te/Deag = TE tunnel Tail-end/Deaggregator
T = Transit LSR
-- = E2E RSVP reservation
== = TE tunnel
4.2. Receipt of E2E Path Message by the Aggregator
The first event is the arrival of the E2E Path message at the
Aggregator. The Aggregator MUST follow traditional RSVP procedures
for the processing of this E2E path message augmented with the
extensions documented in this section.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
The Aggregator MUST first attempt to map the E2E reservation onto a
TE tunnel. This decision is made in accordance with routing
information as well as any local policy information that may be
available at the Aggregator. Examples of such policies appear in the
following paragraphs. Just for illustration purposes, among many
other criteria, such mapping policies might take into account the
Intserv service type, the Application Identity [RSVP-APPID], and/or
the signaled preemption [RSVP-PREEMP] of the E2E reservation (for
example, the aggregator may take into account the E2E reservations
RSVP preemption priority and the MPLS TE tunnel setup and/or hold
priorities when mapping the E2E reservation onto an MPLS TE tunnel).
There are situations where the Aggregator is able to make a final
mapping decision. That would be the case, for example, if there is a
single TE tunnel toward the destination and if the policy is to map
any E2E RSVP reservation onto TE tunnels.
There are situations where the Aggregator is not able to make a final
determination. That would be the case, for example, if routing
identifies two DS-TE tunnels toward the destination, one belonging to
DS-TE Class-Type 1 and one to Class-Type 0, if the policy is to map
Intserv Guaranteed Services reservations to a Class-Type 1 tunnel and
Intserv Controlled Load reservations to a Class-Type 0 tunnel, and if
the E2E RSVP Path message advertises both Guaranteed Service and
Controlled Load.
Whether final or tentative, the Aggregator makes a mapping decision
and selects a TE tunnel. Before forwarding the E2E Path message
toward the receiver, the Aggregator SHOULD update the ADSPEC inside
the E2E Path message to reflect the impact of the MPLS TE cloud onto
the QoS achievable by the E2E flow. This update is a local matter
and may be based on configured information, on the information
available in the MPLS TE topology database, on the current TE tunnel
path, on information collected via RSVP-TE signaling, or a
combination thereof. Updating the ADSPEC allows receivers that take
into account the information collected in the ADSPEC within the
network (such as delay and bandwidth estimates) to make more informed
reservation decisions.
The Aggregator MUST then forward the E2E Path message to the
Deaggregator (which is the Tail-end of the selected TE tunnel). In
accordance with [LSP-HIER], the Aggregator MUST send the E2E Path
message with an IF_ID RSVP_HOP object instead of an RSVP_HOP object.
The data interface identification MUST identify the TE tunnel.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
To send the E2E Path message, the Aggregator MUST address it directly
to the Deaggregator by setting the destination address in the IP
Header of the E2E Path message to the Deaggregator address. The
Router Alert is not set in the E2E Path message.
Optionally, the Aggregator MAY also encapsulate the E2E Path message
in an IP tunnel or in the TE tunnel itself.
Regardless of the encapsulation method, the Router Alert is not set.
Thus, the E2E Path message will not be visible to routers along the
path from the Aggregator to the Deaggregator. Therefore, in contrast
to the procedures of [RSVP-AGG] and [RSVP-GEN-AGG], the IP Protocol
number does not need to be modified to "RSVP-E2E-IGNORE"; it MUST be
left as is (indicating "RSVP") by the Aggregator.
In some environments, the Aggregator and Deaggregator MAY also act as
IPsec Security Gateways in order to provide IPsec protection to E2E
traffic when it transits between the Aggregator and the Deaggregator.
In that case, to transmit the E2E Path message to the Deaggregator,
the Aggregator MUST send the E2E Path message into the relevant IPsec
tunnel terminating on the Deaggregator.
E2E PathTear and ResvConf messages MUST be forwarded by the
Aggregator to the Deaggregator exactly like Path messages.
4.3. Handling of E2E Path Message by Transit LSRs
Since the E2E Path message is addressed directly to the Deaggregator
and does not have Router Alert set, it is hidden from all transit
LSRs.
4.4. Receipt of E2E Path Message by the Deaggregator
Upon receipt of the E2E Path message addressed to it, the
Deaggregator will notice that the IP Protocol number is set to "RSVP"
and will thus perform RSVP processing of the E2E Path message.
As with [LSP-HIER], the IP TTL vs. RSVP TTL check MUST NOT be made.
The Deaggregator is informed that this check is not to be made
because of the presence of the IF_ID RSVP HOP object.
The Deaggregator MAY support the option to perform the following
checks (defined in [LSP-HIER]) by the receiver Y of the IF_ID
RSVP_HOP object:
1. Make sure that the data interface identified in the IF_ID
RSVP_HOP object actually terminates on Y.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
2. Find the "other end" of the above data interface, i.e., X. Make
sure that the PHOP in the IF_ID RSVP_HOP object is a control
channel address that belongs to the same node as X.
The information necessary to perform these checks may not always be
available to the Deaggregator. Hence, the Deaggregator MUST support
operations in such environments where the checks cannot be made.
The Deaggregator MUST forward the E2E Path downstream toward the
receiver. In doing so, the Deaggregator sets the destination address
in the IP header of the E2E Path message to the IP address found in
the destination address field of the Session object. The
Deaggregator also sets the Router Alert.
An E2E PathErr sent by the Deaggregator in response to the E2E Path
message (which contains an IF_ID RSVP_HOP object) SHOULD contain an
IF_ID RSVP_HOP object.
4.5. Handling of E2E Resv Message by the Deaggregator
As per regular RSVP operations, after receipt of the E2E Path, the
receiver generates an E2E Resv message which travels upstream hop-
by-hop towards the sender.
Upon receipt of the E2E Resv, the Deaggregator MUST follow
traditional RSVP procedures on receipt of the E2E Resv message. This
includes performing admission control for the segment downstream of
the Deaggregator and forwarding the E2E Resv message to the PHOP
signaled earlier in the E2E Path message and which identifies the
Aggregator. Since the E2E Resv message is directly addressed to the
Aggregator and does not carry the Router Alert option (as per
traditional RSVP Resv procedures), the E2E Resv message is hidden
from the routers between the Deaggregator and the Aggregator which,
therefore, handle the E2E Resv message as a regular IP packet.
If the Aggregator and Deaggregator are also acting as IPsec Security
Gateways, the Deaggregator MUST send the E2E Resv message into the
relevant IPsec tunnel terminating on the Aggregator.
4.6. Handling of E2E Resv Message by the Aggregator
The Aggregator is responsible for ensuring that there is sufficient
bandwidth available and reserved over the appropriate TE tunnel to
the Deaggregator for the E2E reservation.
On receipt of the E2E Resv message, the Aggregator MUST first perform
the final mapping onto the final TE tunnel (if the previous mapping
was only a tentative one).
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
If the tunnel did not change during the final mapping, the Aggregator
continues the processing of the E2E Resv as described in the four
following paragraphs.
The aggregator calculates the size of the resource request using
traditional RSVP procedures. That is, it follows the procedures in
[RSVP] to determine the resource requirements from the Sender Tspec
and the Flowspec contained in the Resv. Then it compares the
resource request with the available resources of the selected TE
tunnel.
If sufficient bandwidth is available on the final TE tunnel, the
Aggregator MUST update its internal understanding of how much of the
TE tunnel is in use and MUST forward the E2E Resv messages to the
corresponding PHOP.
As noted in [RSVP-AGG], a range of policies MAY be applied to the
re-sizing of the aggregate reservation (in this case, the TE tunnel).
For example, the policy may be that the reserved bandwidth of the
tunnel can only be changed by configuration. More dynamic policies
are also possible, whereby the aggregator may attempt to increase the
reserved bandwidth of the tunnel in response to the amount of
allocated bandwidth that has been used by E2E reservations.
Furthermore, to avoid the delay associated with the increase of the
tunnel size, the Aggregator may attempt to anticipate the increases
in demand and adjust the TE tunnel size ahead of actual needs by E2E
reservations. In order to reduce disruptions, the Aggregator SHOULD
use "make-before-break" procedures as described in [RSVP-TE] to alter
the TE tunnel bandwidth.
If sufficient bandwidth is not available on the final TE tunnel, the
Aggregator MUST follow the normal RSVP procedure for a reservation
being placed with insufficient bandwidth to support it. That is, the
reservation is not installed and a ResvError is sent back toward the
receiver.
If the tunnel did change during the final mapping, the Aggregator
MUST first resend to the Deaggregator an E2E Path message with the
IF_ID RSVP_HOP data interface identification identifying the final TE
tunnel. If needed, the ADSPEC information in this E2E Path message
SHOULD be updated. Then the Aggregator MUST
- either drop the E2E Resv message
- or proceed with the processing of the E2E Resv in the same
manner as in the case where the tunnel did not change (described
above).
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
In the former case, admission control over the final TE tunnel (and
forwarding of E2E Resv message upstream toward the sender) would only
occur when the Aggregator received the subsequent E2E Resv message
(that will be sent by the Deaggregator in response to the resent E2E
Path). In the latter case, admission control over the final tunnel
is carried out immediately by the Aggregator, and if successful the
E2E Resv message is generated upstream toward the sender.
Upon receipt of an E2E ResvConf from the Aggregator, the Deaggregator
MUST forward the E2E ResvConf downstream toward the receiver. In
doing so, the Deaggregator sets the destination address in the IP
header of the E2E ResvConf message to the IP address found in the
RESV_CONFIRM object of the corresponding Resv. The Deaggregator also
sets the Router Alert.
4.7. Forwarding of E2E Traffic by the Aggregator
When the Aggregator receives a data packet belonging to an E2E
reservations currently mapped over a given TE tunnel, the Aggregator
MUST encapsulate the packet into that TE tunnel.
If the Aggregator and Deaggregator are also acting as IPsec Security
Gateways, the Aggregator MUST also encapsulate the data packet into
the relevant IPsec tunnel terminating on the Deaggregator before
transmission into the MPLS TE tunnel.
4.8. Removal of E2E Reservations
E2E reservations are removed in the usual way via PathTear, ResvTear,
timeout, or as the result of an error condition. When a reservation
is removed, the Aggregator MUST update its local view of the
resources available on the corresponding TE tunnel accordingly.
4.9. Removal of the TE Tunnel
Should a TE tunnel go away (presumably due to a configuration change,
route change, or policy event), the Aggregator behaves much like a
conventional RSVP router in the face of a link failure. That is, it
may try to forward the Path messages onto another tunnel, if routing
and policy permit, or it may send Path_Error messages to the sender
if a suitable tunnel does not exist. In case the Path messages are
forwarded onto another tunnel, which terminates on a different
Deaggregator, or the reservation is torn down via Path Error
messages, the reservation state established on the router acting as
the Deaggregator before the TE tunnel went away, will time out since
it will no longer be refreshed.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 20075. IPv4 and IPv6 Applicability
The procedures defined in this document are applicable to all the
following cases:
(1) Aggregation of E2E IPv4 RSVP reservations over IPv4 TE
tunnels.
(2) Aggregation of E2E IPv6 RSVP reservations over IPv6 TE
tunnels.
(3) Aggregation of E2E IPv6 RSVP reservations over IPv4 TE
tunnels, provided a mechanism such as [6PE] is used by the
Aggregator and Deaggregator for routing of IPv6 traffic over
an IPv4 MPLS core.
(4) Aggregation of E2E IPv4 RSVP reservations over IPv6 TE
tunnels, provided a mechanism is used by the Aggregator and
Deaggregator for routing IPv4 traffic over IPv6 MPLS.
6. E2E Reservations Applicability
The procedures defined in this document are applicable to many types
of E2E RSVP reservations including the following cases:
(1) The E2E RSVP reservation is a per-flow reservation where the
flow is characterized by the usual 5-tuple
(2) The E2E reservation is an aggregate reservation for multiple
flows as described in [RSVP-AGG] or [RSVP-GEN-AGG] where the
set of flows is characterized by the <source address,
destination address, DSCP>
(3) The E2E reservation is a reservation for an IPsec protected
flow. For example, where the flow is characterized by the
<source address, destination address, SPI> as described in
[RSVP-IPSEC].
7. Example Deployment Scenarios7.1. Voice and Video Reservations Scenario
An example application of the procedures specified in this document
is admission control of voice and video in environments with a very
high number of hosts. In the example illustrated below, hosts
generate E2E per-flow reservations for each of their video streams
associated with a video-conference, each of their audio streams
associated with a video-conference and each of their voice calls.
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
------ ------
| GW |\ ------- -------- /| GW |
| |\\| | ----- | |//| |
-----| \| Agg | | T | | Deag |/ ------
| |==========================| |
------ /| | | | | |\ ------
| GW |//| | ----- | |\\| GW |
| |/ ------- -------- \| |
------ ------
GW = VoIP Gateway
Agg = Aggregator (TE tunnel Head-end)
Deagg = Deaggregator (TE tunnel Tail-end)
T = Transit LSR
/ = Aggregate Gateway to Gateway E2E RSVP reservation
== = TE tunnel
8. Security Considerations
In the environments concerned by this document, RSVP messages are
used to control resource reservations for E2E flows outside the MPLS
region as well as to control resource reservations for MPLS TE
tunnels inside the MPLS region. To ensure the integrity of the
associated reservation and admission control mechanisms, the
mechanisms defined in [RSVP-CRYPTO1] and [RSVP-CRYPTO2] can be used.
The mechanisms protect the integrity of RSVP messages hop-by-hop and
provide node authentication, thereby protecting against corruption
and spoofing of RSVP messages. These hop-by-hop integrity mechanisms
can naturally be used to protect the RSVP messages used for E2E
reservations outside the MPLS region, to protect RSVP messages used
for MPLS TE tunnels inside the MPLS region, or for both. These hop-
by-hop RSVP integrity mechanisms can also be used to protect RSVP
messages used for E2E reservations when those transit through the
MPLS region. This is because the Aggregator and Deaggregator behave
as RSVP neighbors from the viewpoint of the E2E flows (even if they
are not necessarily IP neighbors nor RSVP-TE neighbors). In that
case, the Aggregator and Deaggregator need to use a pre-shared
secret.
As discussed in Section 6 of [RSVP-TE], filtering of traffic
associated with an MPLS TE tunnel can only be done on the basis of an
MPLS label, instead of the 5-tuple of conventional RSVP reservation
as per [RSVP]. Thus, as explained in [RSVP-TE], an administrator may
wish to limit the domain over which TE tunnels (which are used for
aggregation of RSVP E2E reservations as per this specification) can
be established. See Section 6 of [RSVP-TE] for a description of how
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filtering of RSVP messages associated with MPLS TE tunnels can be
deployed to that end.
This document is based in part on [RSVP-AGG], which specifies
aggregation of RSVP reservations. Section 5 of [RSVP-AGG] raises the
point that because many E2E flows may share an aggregate reservation,
if the security of an aggregate reservation is compromised, there is
a multiplying effect in the sense that it can in turn compromise the
security of many E2E reservations whose quality of service depends on
the aggregate reservation. This concern applies also to RSVP
Aggregation over TE tunnels as specified in the present document.
However, the integrity of MPLS TE tunnels operation can be protected
using the mechanisms discussed in the previous paragraphs. Also,
while [RSVP-AGG] specifies RSVP Aggregation over dynamically
established aggregate reservations, the present document restricts
itself to RSVP Aggregation over pre-established TE tunnels. This
further reduces the security risks.
In the case where the Aggregators dynamically resize the TE tunnels
based on the current level of reservation, there are risks that the
TE tunnels used for RSVP aggregation hog resources in the core, which
could prevent other TE tunnels from being established. There are
also potential risks that such resizing results in significant
computation and signaling as well as churn on tunnel paths. Such
risks can be mitigated by configuration options allowing control of
TE tunnel dynamic resizing (maximum TE tunnel size, maximum resizing
frequency, etc.), and/or possibly by the use of TE preemption.
Section 5 of [RSVP-AGG] also discusses a security issue specific to
RSVP aggregation related to the necessary modification of the IP
Protocol number in RSVP E2E Path messages that traverses the
aggregation region. This security issue does not apply to the
present document since aggregation of RSVP reservation over TE
tunnels does not use this approach of changing the protocol number in
RSVP messages.
Section 7 of [LSP-HIER] discusses security considerations stemming
from the fact that the implicit assumption of a binding between data
interface and the interface over which a control message is sent is
no longer valid. These security considerations are equally
applicable to the present document.
If the Aggregator and Deaggregator are also acting as IPsec Security
Gateways, the Security Considerations of [SEC-ARCH] apply.
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Appendix A - Optional Use of RSVP Proxy on RSVP Aggregator
A number of approaches ([RSVP-PROXY1],[RSVP-PROXY2], [L-RSVP]) have
been, or are being, discussed in the IETF in order to allow a network
node to behave as an RSVP proxy which:
- originates the Resv Message (in response to the Path message) on
behalf of the destination node
- originates the Path message (in response to some trigger) on
behalf of the source node.
We observe that such approaches may optionally be used in conjunction
with the aggregation of RSVP reservations over MPLS TE tunnels as
specified in this document. In particular, we consider the case
where the RSVP Aggregator/Deaggregator also behaves as the RSVP
proxy.
The information in this Appendix is purely informational and
illustrative.
As discussed in [RSVP-PROXY1]:
"The proxy functionality does not imply merely generating a single
Resv message. Proxying the Resv involves installing state in the
node doing the proxy i.e. the proxying node should act as if it had
received a Resv from the true endpoint. This involves reserving
resources (if required), sending periodic refreshes of the Resv
message and tearing down the reservation if the Path is torn down."
Hence, when behaving as the RSVP Proxy, the RSVP Aggregator may
effectively perform resource reservation over the MPLS TE tunnel (and
hence over the whole segment between the RSVP Aggregator and the RSVP
Deaggregator) even if the RSVP signaling only takes place upstream of
the MPLS TE tunnel (i.e., between the host and the RSVP aggregator).
Also, the RSVP Proxy can generate the Path message on behalf of the
remote source host in order to achieve reservation in the return
direction (i.e., from RSVP aggregator/Deaggregator to host).
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The resulting Signaling Flow is illustrated below, covering
reservations for both directions:
|----| |--------------| |------| |--------------| |----|
| | | Aggregator/ | | MPLS | | Aggregator/ | | |
|Host| | Deaggregator/| | cloud| | Deaggregator/| |Host|
| | | RSVP Proxy | | | | RSVP Proxy | | |
|----| |--------------| |------| |--------------| |----|
==========TE Tunnel==========>
<========= TE Tunnel==========
Path Path
------------> (1)-\ /-(i) <----------
Resv | | Resv
<------------ (2)-/ \-(ii) ------------>
Path Path
<------------ (3) (iii) ------------>
Resv Resv
------------> <------------
(1)(i) : Aggregator/Deaggregator/Proxy receives Path message,
selects the TE tunnel, performs admission control over the
TE tunnel. (1) and (i) happen independently of each other.
(2)(ii) : Aggregator/Deaggregator/Proxy generates the Resv message
toward Host. (2) is triggered by (1) and (ii) is triggered
by (i). Before generating this Resv message, the
Aggregator/Proxy performs admission control of the
corresponding reservation over the TE tunnel that will
eventually carry the corresponding traffic.
(3)(iii) : Aggregator/Deaggregator/Proxy generates the Path message
toward Host for reservation in return direction. The
actual trigger for this depends on the actual RSVP proxy
solution. As an example, (3) and (iii) may simply be
triggered respectively by (1) and (i).
Note that the details of the signaling flow may vary slightly
depending on the actual approach used for RSVP Proxy. For example,
if the [L-RSVP] approach was used instead of [RSVP-PROXY1], an
additional PathRequest message would be needed from host to
Aggregator/Deaggregator/Proxy in order to trigger the generation of
the Path message for return direction.
But regardless of the details of the call flow and of the actual RSVP
Proxy approach, RSVP proxy may optionally be deployed in combination
with RSVP Aggregation over MPLS TE tunnels, in such a way that
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RFC 4804 RSVP Aggregation over MPLS TE Tunnels February 2007
ensures (when used on both the Host-Aggregator and Deaggregator-Host
sides, and when both end systems support RSVP):
(i) admission control and resource reservation is performed on
every segment of the end-to-end path (i.e., between source
host and Aggregator, over the TE tunnel between the
Aggregator and Deaggregator that itself has been subject to
admission control by MPLS TE, between Deaggregator and
destination host).
(ii) this is achieved in both directions.
(iii) RSVP signaling is localized between hosts and
Aggregator/Deaggregator, which may result in significant
reduction in reservation establishment delays (and in turn
in post-dial delay in the case where these reservations are
pre-conditions for voice call establishment), particularly
in the case where the MPLS TE tunnels span long distances
with high propagation delays.
Appendix B - Example Usage of RSVP Aggregation over DSTE Tunnels for
VoIP Call Admission Control (CAC)
This Appendix presents an example scenario where the mechanisms
described in this document are used, in combination with other
mechanisms specified by the IETF, to achieve Call Admission Control
(CAC) of Voice over IP (VoIP) traffic over the packet core.
The information in this Appendix is purely informational and
illustrative.
Consider the scenario depicted in Figure B1. VoIP Gateways GW1 and
GW2 are both signaling and media gateways. They are connected to an
MPLS network via edge routers PE1 and PE2, respectively. In each
direction, a DSTE tunnel passes from the Head-end edge router,
through core network P routers, to the Tail-end edge router. GW1 and
GW2 are RSVP-enabled. The RSVP reservations established by GW1 and
GW2 are aggregated by PE1 and PE2 over the DS-TE tunnels. For
reservations going from GW1 to GW2, PE1 serves as the
Aggregator/Head-end and PE2 serves as the Deaggregator/Tail-end. For
reservations going from GW2 to GW2, PE2 serves as the
Aggregator/Head-end and PE1 serves as the Deaggregator/Tail-end.
To determine whether there is sufficient bandwidth in the MPLS core
to complete a connection, the originating and destination GWs each
send for each connection a Resource Reservation Protocol (RSVP)
bandwidth request to the network PE router to which it is connected.
As part of its Aggregator role, the PE router effectively performs
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Initiation Protocol (SIP). These preconditions require that the
participant reserve network resources before continuing with the
session. The reservation of network resources are performed through
a signaling protocol such as RSVP.
Through the collaboration between SIP resource management, RSVP
signaling, RSVP Aggregation and DS-TE as described above, we see
that:
a) the PE and GW collaborate to determine whether there is enough
bandwidth on the tunnel between the calling and called GWs to
accommodate the connection,
b) the corresponding accept/reject decision is communicated to the
GWs on a connection-by-connection basis, and
c) the PE can optimize network resources by dynamically adjusting
the bandwidth of each tunnel according to the load over that
tunnel. For example, if a tunnel is operating at near
capacity, the network may dynamically adjust the tunnel size
within a set of parameters.
We note that admission Control of voice calls over the core network
capacity is achieved in a hierarchical manner whereby:
- DSTE tunnels are subject to Admission Control over the resources
of the MPLS TE core
- Voice calls are subject to CAC over the DSTE tunnel bandwidth
This hierarchy is a key element in the scalability of this CAC
solution for voice calls over an MPLS Core.
It is also possible for the GWs to use aggregate RSVP reservations
themselves instead of per-call RSVP reservations. For example,
instead of setting one reservation for each call GW1 has in place
toward GW2, GW1 may establish one (or a small number of) aggregate
reservations as defined in [RSVP-AGG] or [RSVP-GEN-AGG], which is
used for all (or a subset of all) the calls toward GW2. This
effectively provides an additional level of hierarchy whereby:
- DSTE tunnels are subject to Admission Control over the resources
of the MPLS TE core
- Aggregate RSVP reservations (for the calls from one GW to
another GW) are subject to Admission Control over the DSTE
tunnels (as per the "RSVP Aggregation over TE Tunnels"
procedures defined in this document)
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- Voice calls are subject to CAC by the GW over the aggregate
reservation toward the appropriate destination GW.
This pushes even further the scalability limits of this voice CAC
architecture.
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